1. Technical Field
The invention relates generally to measurement systems, and more particularly, to a method, system and program product to determine a dynamic offset for measurement system matching.
2. Background Art
Efficient semiconductor manufacturing requires highly precise and accurate measurement systems, i.e., metrology instruments. In particular, a measurement system is required to achieve small tolerances to achieve better quality products and fewer rejections in the manufacturing process. There are a number of challenges currently facing the industry relative to measurement systems. One challenge is correctly assessing the measurement potential of a measurement system and matching the measurement system to other measurement systems. Conventionally, when a stable artifact (NIST traceable) is not available, a plurality of measurement systems are matched by having each system test measuring a particular artifact on a monitor wafer, and then determining an offset for each measurement system from a median of all of the measurement systems test measurements. An offset is a correction value, e.g., −2.2 nm, for each measurement. A monitor wafer is a wafer used for measurement testing that includes “artifacts” or structures having a measurable dimension, e.g., thickness, thereon. Typically, artifacts on a monitor wafer are generated to represent variations in a particular semiconductor process of interest for the particular measurement system under test (MSUT). Unfortunately, it is oftentimes difficult to separate the inherent noise associated with the measurement systems data from real process excursions with a high confidence level. As a result, offsets for a measurement system are oftentimes inaccurate. One approach to address the matching problem has been to limit the measurement systems on which a critical dimension is measured during production. Even though this approach results in more uniform measurements, this solution is not desirable because it reduces throughput and increases the risk to a production line by the use of a limited number of measurement systems to support a potentially critical process.
Another challenge relative to measurement system matching is addressing changes in artifacts on monitor wafers over time, which frustrates the ability to match measurement systems. For example, in the semiconductor industry the thickness of a thin-gate oxide film on the surface of a silicon wafer is known to change over time due to environmental conditions. As a result, measurements of an artifact made of that material changes over time, and creates inaccuracies for static measurement system offsets.
In view of the foregoing, there is a need in the art for a solution to the problems presented by the related art.